The present invention relates to a push-button switch device and in particular, to a push-button switch device suitable far equipment incorporating a large number of push-button switches such as pendant switches.
FIG. 19 depicts the electric circuit of a 2-step type push-button switch for controlling an inverter used generally for a pendant switch. The push-button switch device 100 consists of a switch unit 101 and an output unit connected to an AC source at respective R and S terminals. The switch unit 101 is provided with two push-button switches PBa, PBb. The push-button switch PBa is provided with a 1st-stage switch 103 and a 2nd-stage switch 104 while the push-button switch PBb has a 1st-stage switch 105 and a 2nd-stage switch 106. FIG. 19 shows an example in which the 2nd-stage switches of the both push-button switches transmit a same signal and are connected to one same transmitting line a1.
With this arrangement, the 3 kinds of signals transmitted by the switch unit 101 are connected with the output unit 102 by transmitting lines a1, a2, a3, respectively, and the output unit 102 works with the signals from the switch unit 107 through detecting members 107, 108, 109 each formed by a by photocoupler, for example, provided for the respective transmitting lines, so as to transmit operating signals. Namely, the 3 transmitting lines a1, a2, a3 are required to transmit 3 different kinds of signals. For that reason, equipment incorporating a large number of push-button devices in one operating unit such as a pendant switch for operating a crane, hoist, etc., for example, requires wires of a number at least 3 times larger than the number of push-button switch devices plus one common line.
In that case, there is no problem if the number of push-button switch devices incorporated in the pendant switch, etc. is small. In recent times, however, inverter control is being increasingly used in place of the electromagnetic contactor and the specifications of pendant switch are becoming more an more complicated with incorporation of a buzzer switch or switching between linked operation and single operation, etc. Therefore, there is a general tendency for multi-point construction of the pendant switch and multi-stage construction of individual switches. This leads to an increase in the number of cable wires, an increase in the outer dimensions of the pendant switch and an increase in the weight of the cable itself. As a result, the wire bundle becomes rigid and makes the operation of pendant switch difficult in some cases.